This invention relates to a system and method for charging a high voltage bus within a hybrid electric vehicle and more particularly, to a system and method which utilizes a state machine algorithm to control the high voltage contactors within a hybrid electric vehicle and which allows for a relatively rapid and smooth charging of the vehicle""s high voltage bus.
Hybrid electric vehicles (xe2x80x9cHEVsxe2x80x9d) utilize both an internal combustion engine and one or more electric motors to generate power and torque. The electric motors are powered by a source of electrical power, such as one or more batteries or fuel cells. A high voltage bus is used to carry current from the source of electrical power to the electric motor(s) and to other high voltage subsystems and components. Connection of the high voltage bus to the source of electrical power is achieved through several relays or contactors which are controlled by a vehicle system controller.
Particularly, a pre-charge contactor is used to connect the bus to the battery through a resistor, which charges the bus up to the full battery voltage while charging the motor storage capacitors. When xe2x80x9cpre-chargingxe2x80x9d is complete, the main current-carrying contactors are closed, which causes a voltage ripple in the bus due to the current draw from the high voltage subsystem components. When the bus voltage becomes stable, the high voltage subsystem is declared operational and the vehicle may be operated. It is desirable to charge the high voltage bus as fast as possible without risking damage to the system or any of its components, so that the vehicle may be operational without any significant or unnecessary delay. While prior bus-charging strategies are effective to fully charge the high voltage bus, they do not always charge the bus in the most rapid or efficient manner. Additionally, these prior strategies do not always accurately determine of the point in time when the high voltage bus within a hybrid electric vehicle becomes stable and capable of powering the high voltage vehicle components. As a result, these prior strategies do not allow the vehicle to be operational in the shortest amount of time possible.
There is therefore a need for a system and method for charging a high voltage bus within a hybrid electric vehicle which allows for the high voltage bus to be fully charged in a relatively rapid and efficient manner without any significant or unnecessary delay.
A first non-limiting advantage of the present invention is that it allows for an accurate and timely determination of the point of time when the high voltage bus within a hybrid electric vehicle becomes stable and capable of powering the high voltage vehicle components.
A second non-limiting advantage of the present invention is that it allows for the determination of error conditions within the bus-charging process by indicating when the monitored charging sequence differs significantly from the expected charging sequence.
A third non-limiting advantage of the invention is that it provides a system and method for charging a high voltage bus within a hybrid electric vehicle which reduces the overall time required for the high voltage subsystem to become operational.
According to a first aspect of the present invention, a system is provided for charging a high voltage bus within a vehicle. The system includes a source of electrical power; a pre-charge contactor which is coupled to the source of electrical power and to the high voltage bus, and which is effective to selectively and operatively connect the high voltage bus to the source of electrical power; a main contactor which is coupled to the source of electrical power and to the high voltage bus, and which is effective to selectively and operatively connect the high voltage bus to the source of electrical power; a voltage sensor which is effective to measure a voltage of the high voltage bus and to generate signals in response to the measured voltage; and a controller which is communicatively coupled to the pre-charge contactor, to the main contactor and to the voltage sensor, the controller being effective to receive the signals and to use the signals to calculate the voltage of the high voltage bus and the change in voltage over time of the high voltage bus, the controller being further effective to utilize the calculated voltage and change in voltage over time within a state machine strategy to close the pre-charge contactor and the main contactor, thereby selectively charging the high voltage bus.
According to a second aspect of the present invention, a method is provided for charging a high voltage bus within a vehicle including a source of electrical power and a pre-charge contactor and a main contactor which selectively connect the source of electrical power to the high voltage bus. The method includes the steps of monitoring the voltage of the high voltage bus; monitoring the change in voltage over time of the high voltage bus; and using the monitored voltage and the monitored change in voltage over time within a state machine strategy to determine when to close the pre-charge contactor and the main contactor.
Further objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred embodiment of the invention and by reference to the following drawings.